An integrated gas unit is formed by integrating a plurality of gas supply lines. The integrated gas unit is, for example, connected to a reaction vessel to regulate one or more than one gas which is to be supplied to the vacuumed reaction vessel through the gas supply lines. A flow rate of operation gas to be supplied to the reaction vessel exerts influence on product quality. For this reason, each of the gas supply lines includes a mass flow controller to measure the flow rate and a flow rate regulation valve operative to make a flow rate value measured by the mass flow controller agree with a set flow rate. The mass flow controller is, for example, configured to measure the flow rate based on a temperature difference between an upstream side and a downstream side of a thin inner pipe through which the operation gas flows. When products of the operation gas adhere to an inside wall of the inner pipe and thereby an inner diameter of the pipe changes, there occurs an error (difference) in the measured value measured by the mass flow controller. In response to this, the integrated gas unit is configured to verify each flow rate of the respective mass flow controllers one at a time by use of a flow rate verification unit.
FIG. 8 is a circuit diagram of a conventional flow rate verification unit 101 and a conventional integrated gas unit 110. The integrated gas unit 110 is provided with a purge gas line 111 to regulate purge gas and first to third gas supply lines 121A, 121B, and 121C. The purge gas line 111 is provided with a purge gas input port 117 to input the purge gas and connected with a regulator 112, a Bourdon pressure gauge 113, a pressure gauge 114, a first purge valve 115, and a second purge valve 116 in series in this order from an upstream side. The first gas supply line 121A is provided with a gas input port 127A to input first gas and connected with a pressure gauge 122A, a gas input valve 123A, a mass flow controller (MFC) 124A, and a flow rate regulation valve 125A in series in this order from the upstream side. The first gas supply line 121A is further provided with a purge gas input valve 126A between the gas input valve 123A and the mass flow controller 124A to control input of the purge gas which has branched off and flown from the purge gas line 111. The second and third gas supply lines 121B and 121C are configured similarly to the first gas supply line 121A. The purge gas line 111 and the first to third gas supply lines 121A to 121C are arranged in parallel to a common output valve 131 via a common passage 130.
The flow rate verification unit 101 is provided with a first shutoff valve 102, a pressure gauge 103, a thermometer 104, and a second shutoff valve 105. The first shutoff valve 102 is connected to the common passage 130. When flow rate verification of the mass flow controller 124A is to be performed, for example, the flow rate verification unit 101 is controlled to bring each of the gas input valves 123A to 123C, the second purge valve 116, the flow rate regulation valves 125B and 125C, the common output valve 131, and the second shutoff valve 105 into the valve-closed state and bring each of the first purge valve 115, the purge gas input valve 126A, the flow rate regulation valve 125A, and the first shutoff valve 102 into the valve-open state. The flow rate verification unit 101 subsequently executes the control to flow purge gas into the mass flow controller 124A so that the second purge valve 116, the flow rate regulation valves 125A to 125C, the common output valve 131, and the second shutoff valve 105 are filled with the purge gas. The flow rate verification unit 101 obtains a pressure increased value during a measurement time from a pressure measured value measured by the pressure gauge 103 and calculates an absolute flow rate of the mass flow controller 124A from values of the obtained pressure increased value, the temperature measured value measured by the thermometer 104, the measurement time, and a volume V among the second purge valve 116, the flow rate regulation valves 125A to 125C, the common output valve 131, and the second shutoff valve 105. The flow rate verification unit 101 further obtains the difference between the calculated absolute flow rate and the set flow rate and calibrates the set flow rate in a case that the difference is within an allowable range between a normal range and an abnormal range. When the difference falls in the abnormal range, the flow rate verification unit 101 makes an indication to indicate an instruction to replace the mass flow controller 124A.
Each integrated gas unit 110 has the same circuit configuration, but a volume V1 among the second purge valve 116, the flow rate regulation valves 125A to 125C, the common output valve 131, and the first shutoff valve 102 varies according to units by tolerances of constituent components, assembling tolerances, and other reasons (the volume V1 is also called “tank volume V”). Variations in the tank volume V1 correspond to variations in the volume V, leading to a decline in accuracy of the flow rate verification.
To address the above, the conventional flow rate verification unit 101 is configured to, for example, bring the first purge valve 115, the purge gas input valve 126A, the flow rate regulation valve 125A, and the first shutoff valve 102 into the valve-open state, bring the flow rate regulation valves 125B and 125C, the purge gas input valves 126B and 126C, the common output valve 131, and the second shutoff valve 105 into the valve-closed state, and then supply purge gas to the purge gas line 1 and obtain the pressure increased value per unit time from when the pressure gauge 103 measures the predetermined initial pressure to when the pressure gauge 103 measures the target value. The volume V is thus calculated based on the pressure increased value and the temperature measurement value measured by the thermometer 104. A volume V2 between the first shutoff valve 102 and the second shutoff valve 105 has been known in advance (the volume V2 is also called “known volume V2”), and hence the flow rate verification unit 101 calculates the tank volume V1 by subtracting the known volume V2 from the volume V. As a result of this, the variations in the tank volume V1 are reflected on the flow rate verification of the mass flow controllers 124A to 124C (see Patent Document 1, for example).